can/can't/could/couldn't for abilities

I don't can play the guitar.

(a)  

She cans speak four languages.

(a)  

How fast you can swim?

(a)  

I could ran very fast when I was a child.

(a)  

I didn't could understand what he said.

(a)  

Does he can cook? Yes, he can.

(a)  

Could he walk before his accident? Yes, he did.

(a)  

I couldn't to swim when I was a child.

(a)  

Later, we can playing football.

(a)